As wireless devices such as a wireless user equipment (UE) become indispensible in daily life, an increased accuracy in locating a UE is demanded for the wireless phone service. For example, the US Federal Communication Commission (FCC) requires that an emergency call from a UE be located within 50 meters for 67% of wireless calls and within 150 meters for 95% of wireless calls. One approach to achieving the desired positioning accuracy is to use network assisted observed time difference of arrival (OTDOA) for positioning 3rd Generation Partnership Project (3GPP) long-term evolution (LTE) compliant wireless devices. Based on this approach, the differences in the time of arrival of known signals sent from nearby cells are measured at the UE and the position of the UE is calculated based on the differences of arrival times. The UE may need measure these arrival time differences and report them to the network.
The signals the UE receives for the positioning purpose are called positioning reference signals (PRS). Depending on the transmission bandwidth, the positioning reference signals may be received at the UE over multiple subframes such as NPRS=1, 2, 4 or 6 subframes for each positioning occasion where one LTE subframe lasts 1 millisecond (Ins). One positioning occasion is a time duration that may occur every TPRS=k*160 ms (k=1, 2, 4 or 8) for the UE to receive the positioning reference signals. All nearby cells involved in the positioning procedure transmit synchronously their positioning reference signals so that the signals overlap in time as much as possible. The UE may have up to M positioning occasions to measure all positioning reference signals from the nearby cells in one frequency carrier and report these measurements to an associated enhanced Serving Mobile Location Center (eSMLC). The number of positioning occasions M that the UE may have to measure positioning reference signal sent from nearby cells may vary and for example may range from 4 to 16, according to a 3GPP specification.